Comparative effectiveness of hydrophobizing and crystallizing additives effects on the properties of gypsum-cement-pozzolanic binder and concrete based on it

The water resistance of concrete based on gypsum-cement-pozzolanic binder (GCPB) plays a critical role in ensuring the durability of products and structures, so finding new ways to increase it is one of the key tasks for these materials. Today, the most widespread method of modifying GCPB concrete with chemical additives that belong to the class of water-repellent according to GOST 24211–2008, giving it water-repellent properties. However, recently, especially abroad, so-called hydrophilic crystalline additives have become in demand, which are used to increase the water resistance grade of concrete. It is achieved by clogging its microstructure with needle-shaped new formations formed during the chemical interaction of the components of the additive with the hydration products of clinker minerals of the cement binder. The work carried out a comparative assessment of the effectiveness of six types of foreign chemical additives belonging to the class of hydrophobic and hydrophilic on such properties of GCPB concrete as strength, density, water absorption, water resistance according to the softening coefficient. It was established that the hydrophilic crystalline additive “Flocrete WP Crystal” showed the greatest efficiency for GCPB concrete, which, at a dosage of 2% by weight of the binder, significantly increased the softening coefficient (1.09) and reduced water absorption (3.2%) in comparison with non-additive GCPB-concrete (0.89 and 7.2%, respectively). Obviously, this will increase the durability of GCPB concrete and open up new possibilities for practical application in construction.